I have been reading various articles and most state that treatment with CaCl2 produces higher efficiency of transformation than MgCl2. Can anyone explain why Ca2+ is better than Mg2+ at neutralizing the negative charge of the plasma membrane of bacteria such as E. coli? Or why divalent cations are better than monovalent cations (such as K+ or Na+)?
Thanks very much!
Divalent cactions are more stable than monovalent actions. Mg+2 can be used for more purposes especially beneficial. Ca+2 are important for cellular purposes and helps to keep off bacteria. Mg+2 contributes and does not always help (bacteria may use it for its outer membrane). Cl- is used either way (stability)
Hello, as DNA is a highly hydrophilic molecule, normally it cannot pass through the cell membrane of bacteria. Hence, in order to make bacteria capable of internalizing the genetic material, they must be made competent to take up the DNA. This can be achieved by making small holes in bacterial cells by suspending them in a solution containing a high concentration of calcium. Extra-chromosomal DNA will be forced to enter the cell by incubating the competent cells and the DNA together on ice followed by a brief heat shock that causes the bacteria to take up the DNA. Additionally, a poorly performed procedure may lead to not enough competence cells to take up DNA. The divalent cations generate coordination complexes with the negatively charged DNA molecules and LPS, the monovalent that you mentioned can't. DNA, being a larger molecule, cannot itself cross the cell membrane to enter into the cytosol. The heat shock step strongly depolarizes the cell membrane of CaCl2-treated cells. Thus, the decrease in membrane potential lowers the negativity of the cell’s inside potential which ultimately allows the movement of negatively charged DNA into the cell’s interior.
Hope this info will help you.
Goof luck!
Hello Fabiana
Competency can be induced using salt solutions of different cations, but the difference will be only in their transformation efficiency. Please refer to the research paper below for more information.
Karuna et al., World J Pharm Sci 2015; 3(4): 732-736
I hope it is helpful.
Regards.
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